Business Due Diligence Checklist for Buyers (UK)

Business due diligence is the structured investigation a buyer runs on a target company before signing. You're checking that what the seller claims about the finances, the contracts, the customers and the staff is actually true. Think of it as the gap between the story in the listing and the reality in the filing cabinet. Closing that gap is the whole job.

Here's why it matters in numbers. The five-year survival rate for UK businesses born in 2019 was just 38.4%, according to ONS Business Demography 2024. Most businesses don't make it to year five. When you buy one, you're inheriting whatever's already gone wrong: undisclosed debt, a wobbly key customer, a lease that's about to be reviewed upwards, a star employee who's already half out the door. Diligence is how you find those things while you can still walk away or knock the price down, rather than after the money's gone.

A quick distinction people muddle. Buyer-side diligence is what you commission to protect yourself. Vendor due diligence is what a seller commissions to pre-empt your questions and speed the sale up. They cover similar ground; the difference is who's paying and whose interests the report serves. Never treat a vendor's report as a substitute for your own checks.

The scope splits into four pillars: financial, legal, commercial and operational. A small sole-trader café needs a lighter touch than a £2m limited company with twelve staff and a warehouse lease, but the categories are the same. Skip one and you'll find out which one mattered after completion, usually at the worst possible moment. This guide walks each pillar in turn, then hands you the full checklist as a table you can work straight off. If you're earlier in the process and still sizing up a target, start with how to analyse a business before buying it.

Financial due diligence is the part where you verify the company actually earns what the seller says it earns, and works out what it really owes. It's the pillar that most often changes the price, so it's where most of your accountant's hours should go.

Start with three years of full accounts plus the most recent management figures. For a limited company you can pull the filed accounts, the confirmation statement, the officers and any registered charges straight off Companies House for free before you ask the seller for anything. Cross-check what's filed against what you're handed. They should reconcile. When they don't, you've found your first question.

Normalising the profit in financial due diligence

Reported profit is rarely the profit you'd run the business on. The job is to work out normalised EBITDA, earnings before interest, tax, depreciation and amortisation, adjusted for the quirks of owner-managed companies. Owner-managers run personal costs through the business and pay themselves in ways that suit their tax position, not yours. So you add back and strip out:

• An owner's salary that's well below or well above a market rate for the role
• One-off costs that won't recur (a legal dispute, a relocation, a bad-debt write-off)
• Personal expenses dressed as business costs: the spouse on payroll who never appears, the family car, the "client entertainment" that's suspiciously seasonal
• Related-party transactions priced at something other than arm's length

The normalised figure is what a multiple gets applied to.

Get the normalised EBITDA wrong by £20k and on a 4x multiple you've mispriced the business by £80k. This is exactly why a buyer with a six-figure deal shouldn't do the numbers alone.

Debt, working capital and the cash trap

Profit isn't cash. A business can look profitable and still be strangled by working capital. Pull the aged debtors and creditors. Are customers paying in 30 days or 90? Is the company quietly funding itself by stretching its suppliers, a balance that becomes your problem the day you take over?

Then the debt. List every liability: bank loans, asset finance, director's loans, tax owed to HMRC, deferred VAT, overdrafts, and the off-balance-sheet ones like a personal guarantee the owner has given that the bank will want re-papering. The structure of the deal matters here. In a share purchase you inherit the liabilities; in an asset purchase you can often leave most behind. We go deep on this in buying a business with debt and liabilities, and it's worth reading before you choose your deal structure.

Last thing: get the VAT and PAYE position confirmed in writing, ideally with HMRC statements. Unpaid tax has a habit of surfacing after completion, and HMRC is not a creditor you can negotiate with the way you might a supplier.

Legal due diligence checks that the company owns what it claims to own, isn't bound by terms that wreck the economics, and isn't carrying a lawsuit you don't know about. This is your solicitor's territory, but you should understand what they're looking for so you can brief them properly.

Contracts and change-of-control

The single most important thing your solicitor reads is the change-of-control clause in the company's key contracts. Plenty of customer and supplier agreements say the contract can be terminated if the business changes hands. If your target's biggest customer has that clause and the seller hasn't sounded them out, you might buy a business and lose 40% of its revenue in the first month.

A termination-on-sale clause in the contract of your largest customer is one of the most common ways an acquisition blows up. Get the material contracts read, list every change-of-control clause, and get written comfort from the counterparties before you sign.

Intellectual property and assets

Does the company actually own its brand, its domain names, its software, its designs? You'd be surprised how often the website domain is registered to the founder's personal email, or the logo was knocked up by a freelancer who never signed over copyright. Check trade mark registrations, domain ownership, and that any code or creative work was either made by employees or properly assigned in writing. If IP is the reason you're buying, this check isn't optional.

Litigation, leases and consents

Ask for a schedule of current, threatened and recent disputes, and don't just take "none" at face value; cross-check against the accounts for legal provisions. For the lease, the things that bite are the unexpired term, the rent and any review date, the repair obligations (a full repairing and insuring lease can be a five-figure surprise), and above all whether the landlord's consent is needed to assign it to you. A short lease with a review next quarter is a completely different proposition from a ten-year lease at a fixed rent. Finally, check the company holds every licence, permit and regulatory consent it trades on, and that those transfer with the deal. A restaurant without a current premises licence isn't a restaurant; it's a room with tables.

Commercial due diligence steps back from the documents and asks the harder question: is this a good business in a market that'll still be here in five years, or a tired one coasting on a founder's old relationships? Financial diligence tells you what happened. Commercial diligence tells you whether it'll keep happening once you're the owner. The ICAEW published its first dedicated commercial due diligence guideline in September 2025, which tells you the profession now treats it as a discipline in its own right, not an afterthought.

Customer concentration, the one that catches people out

Get a revenue breakdown by customer for the last two or three years. The number you're hunting for is the share held by the top one, three and five customers. If one client is 40% of revenue, you don't own a business so much as a single relationship that happens to have staff attached. And relationships travel with people. Ask the obvious follow-ups: how long has each big customer been with the company, are they on a contract or rolling month to month, and is the relationship with the company or personally with the seller who's about to leave? A founder who golfs with the buyer at the top account is a risk you need priced in.

Pipeline, market and competition

Look past the existing book to where the next pound comes from. Is there a sales pipeline, or has nothing new closed in eighteen months? Is the market growing, flat or quietly shrinking? Who are the three competitors that could take share, and is a bigger player or a cheaper online model circling the niche? You're not trying to forecast the future precisely. You're trying to avoid buying a buggy-whip maker in 1910. Talk to a few customers if the seller will allow it under NDA; thirty minutes on the phone with two clients tells you more about retention than any spreadsheet. Pair this with the questions to ask when buying a business, which gives you the script for those conversations.

Operational and people due diligence checks whether the business can keep running after the seller hands over the keys. A company can have clean accounts and loyal customers and still fall apart on day one because everything that mattered lived in the founder's head. This is the pillar buyers skip most often and regret most reliably.

Key-person risk and handover

The first question is brutally simple: what happens the morning the owner stops answering the phone?

If the seller is the chief salesperson, the head of operations, the keeper of every supplier password and the only person the long-standing customers will speak to, you're not buying a business. You're buying a job that depends on someone who's leaving. Map who does what, identify single points of failure, and build a proper handover and a non-compete into the deal. A seller who'll stay on for three to six months and is contractually barred from setting up next door is worth a lot.

People and TUPE

When you buy a business as a going concern, employees usually come with it, and their rights are protected. Under the UK rules covering transfers and takeovers, employees' jobs transfer to the new owner, their existing terms and conditions transfer with them, and their continuity of service is preserved. You can't quietly cut their holiday entitlement or notice period the week after completion, and there are obligations to inform and consult staff before the transfer. So you need the full employee list with start dates, salaries, contracted hours, holiday accrued and any outstanding grievances or disciplinary matters. Get your solicitor to confirm whether these regulations apply to your deal. They usually do for an asset purchase of a trading business, and getting it wrong is expensive.

Systems, suppliers and dependencies

List the systems the business runs on (accounting, CRM, e-commerce, the booking software) and check what transfers and what's tied to the seller's personal accounts or licences. Same for suppliers: is the company dependent on one supplier with no alternative, and are those terms in writing or a handshake the seller's been relying on for fifteen years? Handshakes don't transfer. Walk the premises if there are any. Kit that looks fine on a spreadsheet can be held together with tape in person, and equipment you'll have to replace in year one is a cost you should be negotiating now, not discovering later.

Vendor due diligence is a report the seller commissions on their own business, before it goes to market, so that buyers get answers to the obvious questions up front. On larger or competitive sales it speeds everything up and props up the asking price, because a buyer who can see a clean independent report has fewer reasons to chip the price or drag the process out.

The catch: vendor diligence is paid for by the seller and written to present the business in the best honest light. That doesn't make it dishonest, but it does mean it's not your report. Read it, take the time it saves you, and then run your own checks on anything material. If the vendor report is a year old, treat its numbers as a starting point and re-verify the recent trading yourself. Be wary, too, of a report that's all sunshine and no risk section. Every real business has risks, and a diligence report that can't name any wasn't looking hard.

What a data room is

A data room is the secure online folder where the seller drops the documents you've asked for (accounts, contracts, leases, employee details, the lot) so you and your advisers can review them without boxes of paper changing hands. For a small deal it might be a shared Google Drive; for a larger one, a purpose-built virtual data room with access logs. Either way, the quality of the data room is itself a signal. A seller who hands you a clean, well-organised, complete folder within a week is usually running a tight ship. A seller who dribbles documents out one at a time, can't find the lease, and keeps promising the management accounts "next week" is telling you something about how the business is run, and possibly about what they'd rather you didn't see in one sitting.

Keep your own index of what you requested, what's been provided, and what's outstanding. At completion that list becomes part of the paper trail, and the gaps in it become the warranties and indemnities your solicitor negotiates into the purchase agreement. Anything the seller won't or can't evidence, you push into a warranty so that if it turns out to be untrue, you have a contractual claim rather than a hard lesson.

Here's the working checklist. Use it as your data-room request list and your review tracker. For each area, you request the item, review it, and flag against the red flag that should make you stop and dig. This is the due diligence checklist when buying a business that I'd hand a first-time buyer. Adjust the depth to the deal size, but don't drop the categories.

Area	What to request	Red flag to watch for
Filed accounts	3 years' statutory accounts + Companies House filing history	Late filings, sudden restatements, qualified audit opinion
Management accounts	Latest 12 months, monthly	None exist, or they don't reconcile to the filed accounts
Profit normalisation	Add-backs schedule, director's pay, one-offs	Big unexplained add-backs that inflate EBITDA
Bank statements	12+ months for the trading account	Statements don't match declared turnover
Debt & liabilities	Loans, asset finance, director's loans, HMRC position	Undisclosed debt, deferred VAT, personal guarantees
Working capital	Aged debtors and creditors	Funding the business by stretching suppliers
Tax	VAT, PAYE and corporation tax statements	Arrears, open enquiries, late payments to HMRC
Key contracts	Customer and supplier agreements	Change-of-control or termination-on-sale clauses
Customer concentration	Revenue by customer, 2 to 3 years	One customer above ~25-30% of revenue
Intellectual property	Trade marks, domains, software assignments	IP owned by the founder personally, not the company
Litigation	Schedule of current and threatened disputes	Active claim, or a gap vs. provisions in the accounts
Lease & property	Lease, term, rent reviews, repair obligations	Short term, imminent review, landlord consent needed
Licences & consents	Trading licences, regulatory permits	Lapsed or non-transferable licence
Employees	List with terms, holiday, grievances	Key-person dependency, undisclosed disputes
Systems & suppliers	Software access, supplier terms	Logins tied to the seller, sole-supplier dependency
Insurance	Current policies and claims history	Lapsed cover, frequent claims, no cover at all

Work top to bottom, tick what reconciles, and ring the items that don't. The unticked rows are your negotiation list. If you want the lighter version for a sub-£30k sole-trader deal, the shorter checklist in how to analyse a business before buying covers the essentials.

Some findings are negotiating points; others are reasons to walk. Knowing the difference is most of the skill. A red flag rarely means "never buy" on its own. It means "don't move another step until this is explained and evidenced." Here are the ones that have ended deals, and rightly so.

• The accounts don't reconcile to the bank. If declared turnover and the actual money landing in the account are more than a few percent apart with no clean explanation, stop. Either the figures are wrong or someone's massaging them, and neither is a base to value a business on.
• The seller can't or won't evidence something material. "Trust me, it's all there" is not diligence. When a seller stonewalls on the key customer's contract, the HMRC position, or twelve months of statements, assume the worst case and price it in, or leave.
• A single customer dominates the revenue and the relationship is personal. One client at 40% who deals only with the departing owner is the classic post-completion collapse. Either get that relationship contracted and transferred before you sign, or treat the revenue as at risk.
• Undisclosed debt or tax arrears surface mid-process. Finding a deferred VAT balance or a director's loan the seller "forgot" tells you two things: there's debt, and the seller isn't straight. The second is worse than the first.
• The filing history is a mess. Late or overdue statutory filings aren't just untidy. Miss a confirmation statement and a company can be fined up to £5,000 and struck off the register. Persistent lateness is a tell about how the whole business is run.
• The story keeps changing. The reason for sale was retirement, then it was health, now it's "new opportunities." When the narrative shifts under questioning, the truth is usually the version that makes the business worth less.

None of these mean the deal is dead automatically. They mean you pause, get the answer in writing, and either solve it in the contract through price, warranties or indemnities, or you walk. The buyers who get burned are almost always the ones who saw the flag, felt the sunk cost of weeks of work, and pressed on anyway.

After due diligence comes the part where what you found gets turned into deal terms and, eventually, a signed contract and money moving. Diligence isn't a box-tick before an offer you'd make anyway. It's the evidence that shapes the offer. So let's walk the sequence.

Most UK deals run heads of terms first: a short, mostly non-binding document setting out price, structure and the headline conditions, often with an exclusivity period so you're not doing diligence while the seller shops the business around. Then diligence proper, which on an SME typically runs around six to twelve weeks depending on how clean the data room is and how responsive everyone stays.

What you found feeds straight into three levers:

• Price. A weaker normalised EBITDA, a lease liability or a wobbly key customer is a reason to revise the offer down. This is where your accountant's normalisation work earns its fee.
• Structure. Heavy undisclosed liabilities might push you from a share purchase to an asset purchase, or towards a deferred payment or earn-out that ties some of the price to the business actually performing after you take over.
• Warranties and indemnities. Anything the seller couldn't fully evidence becomes a promise written into the sale and purchase agreement, with a financial claim attached if it turns out to be untrue. Your unticked checklist rows become these clauses.

Then the solicitors draft the share or asset purchase agreement, you agree the warranties and the disclosure letter (where the seller formally lists exceptions to those promises), funds and any finance are arranged, and you exchange and complete, sometimes the same day, sometimes with completion conditional on a consent like a lease assignment. If you're working out how to fund the gap between your cash and the price, read how to finance buying a business in the UK before you firm up the offer, because your funding structure and your deal structure have to agree with each other.

The through-line is simple: good business due diligence doesn't just protect you from a bad deal, it gives you the bargaining power to make a fair one. When you've done the work and you can point to the schedule, the statement, the clause, you negotiate from evidence instead of hope. Ready to put it into practice? Browse businesses for sale on NewOwner and run this checklist against the first one that catches your eye.